Particulate laundry compositions containing both anionic sulphonate- and sulphate-type surfactants and ethoxylated alcohol nonionic surfactants are very well-known. Whilst anionic surfactants such as alkylbenzene sulphonates are very robust and can readily be incorporated into detergent powders both by high-temperature processes, for example, spray-drying, and by lower-temperature non-tower mixing and granulation processes, the options for incorporating nonionic surfactants are more limited, especially for the more hydrophobic ethoxylates having a low degree of ethoxylation. These are not generally incorporated in significant quantities into slurries and spray-dried because of emission problems. In non-tower granulated powders, combination of nonionic surfactants in significant quantities with anionic surfactants, builders and other ingredients in a base granule has led to problems of poor dispersion and dissolution in the wash, possibly due the formation of gel-like liquid crystal phases.
It is therefore desirable to add nonionic surfactant to granular detergent compositions made by both tower (spray-drying) and non-tower processes after the base granulates (base powders) have been formed. The lower-ethoxylated nonionic surfactants are liquids or waxy solids at ambient temperature and can be sprayed onto the base powder. This works well if the loading of other organic materials, for example, anionic surfactant, in the base powder is relatively low so that there is some porosity available to take up the sprayed-on nonionic surfactant. However, if the anionic surfactant loading of the base powder is high, the spraying-on of nonionic surfactant will lead to an unacceptable deterioration of flow properties, or even to the "bleeding out" of nonionic surfactant from the powder during storage.
An alternative approach is to prepare a separate granule in which the nonionic surfactant is absorbed into, or adsorbed onto, a carrier material, and to admix the separate granule with the base powder. Highly porous carrier materials such as zeolites and silicas have been proposed in the prior art, for example, JP 08 027 498A (Kao), JP 07 268 398A (Lion), and WO 98 54281A (Unilever). Using such materials it is possible to achieve very high loadings of nonionic surfactant on the carrier, for example, at least 55 wt %.
It has been found, however, that these granular materials, while excellent for detergent compositions intended for use in machine washing, are not ideal for use in compositions intended for low-temperature and/or low-agitation washing conditions, for example, in the handwash, because the solubility and dissolution time may be inadequate.
It has now been discovered that a nonionic surfactant granule having good solubility, high dissolution rate and excellent powder properties may be prepared using, as carrier material, sodium sesquicarbonate formed by in situ neutralisation in the presence of the nonionic surfactant. Although the surfactant loadings achievable are not as high as those obtained with silica carriers, the lower surfactant loadings can be tolerated in formulations where the total content of nonionic surfactant is relatively modest.
It has also been found that compositions containing this nonionic surfactant granule in combination with other granules exhibit improved storage stability of sodium percarbonate bleach.
WO 97 33957A (Amway Corporation) discloses sodium carbonate-based laundry detergent powders of improved solubility, containing a post-added acidulant, for example, adipic, succinic, boric or fumaric acid. Citric acid may additionally be present. Final compositions typically contain 53 wt % sodium carbonate, 22 wt % nonionic surfactant, 7.5 wt % citric acid, and 5 wt % post-added acidulant.
EP 110 588B (Unilever) discloses a free-flowing granular detergent composition comprising a nonionic surfactant, a structuring agent having at least three carboxyl groups (eg citric acid, sodium citrate), and sodium carbonate in very finely divided (micropulverised) form.
WO 93 21292A (Church & Dwight) discloses free-flowing detergent powders containing sodium carbonate, sodium bicarbonate, and low levels of nonionic surfactant (less than 15 wt %).